1. Field of the Invention
The present invention relates to an optical head for an optical recording/reproducing apparatus which is capable of optically recording information on a recording medium and/or optically reproducing the recorded information.
2. Description of the Prior Art
One of the conventional prior systems provides an optical heads which is capable of directly converging a divergent light beam from a light source onto a recording medium with an objective lens. U.S. Pat. No. 4,079,247 discloses an example of the optical head mentioned above. In addition, there are a variety of optical heads which collimate the divergent light beam into a parallel light beam with a collimator lens before converging thereby freeing the apparatus from degradation of optical characteristics even when the objective lens is displaced for focussing or tracking operation or even when an inclined optical border plain exists in the parallel light beam. These optical recording/reproducing apparatuses are disclosed by U.S. Pat. Nos. 4,447,722, 4,466,087 and Japanese Patent Application of Laid-Open No. 60-106038.
The optical head disclosed by U.S. Pat. No. 4,079,247 requires extraction of a detected light beam reflected from the recording medium by separating this beam from the divergent light beam travelling toward the recording medium. This causes a problem that homogeneousness of the detected light beam easily degenerates due to angle-dependency of either a half-mirror or a polarizing beam splitter used for extracting the detected light beam. On the other hand, the optical recording/reproducing apparatuses disclosed by U.S. Pats. No. 4,447,722, 4,466,087 and Japanese patent application of Laid-Open No. 60-106038 require a delicate adjustment of the position of the collimator lens in the optical axis direction. In particular, the optical recording/reproducing apparatus disclosed by the Japanese Patent Application uses a prism having an inclined surface disposed in the path of the collimated parallel light beam, so that unavoidably the position adjustment of the collimator lens must be implemented with an extreme precision.